1. Field of the Invention
The present invention relates generally to an ink-jet printing apparatus and a printing method, and more specifically to an ink-jet printing apparatus achieving high stability in ink ejection for performing high quality printing by ejecting an ink and a liquid containing a substance which makes coloring agent in the ink insoluble or aggregation.
2. Description of the Related Art
Conventionally, there has been proposed an ink-jet printing apparatus performing printing by ejecting an ink toward a printing medium through ejection openings in an ink-jet head by applying heat for the ink by means of a heater to generate bubble in the ink and utilizing a pressure generated by expansion of the bubble.
Recently, for printing a high quality image, it has been proposed to eject a particular liquid onto the printing medium immediately before or immediately after ejecting the ink. The liquid is a transparent and colorless liquid to be mixed with the ink. The liquid and the ink overlapped on the printing medium are admixed on the printing medium before they are absorbed into the printing medium and fixed thereon. In such manner, printing characteristics such as color development ability, water resistance and bleeding prevention ability of the ink in relation to the printing medium can be improved. Particularly, even when the printing medium is a general plain paper, on which an ink receptacle layer is not coated, the liquid demonstrates substantial effect in permitting printing without causing bleeding. Such liquids are called printing improvement liquids.
In the prior art, a problem has been encountered in degradation of quality of a printed image due to bleeding of ink caused by fibers of the paper when printing is performed by ink-jet system on a general plain paper having no coated ink receptacle layer. Such problem is about to be solved by the printing method employing the foregoing printing improvement liquid. For this purpose, various printing improvement liquids have been developed.
All of the printing improvement liquids to be employed for the purpose set forth above have a property to make a coloring agent in the ink insoluble or aggregated, and thus instantly fixed once it is admixed with the ink. Therefore, when the droplet of the printing improvement liquid rebounded from the surface of the plain paper or mist thereof contacts with a face of an ejection head, the printing improvement liquid can be fixed on the face to cause a problem of blocking of ink ejection openings.
Next, the foregoing problem will be specifically explained with reference to the drawings.
FIGS. 3A and 3B are front elevation views showing constructions of ink-jet printing heads, in each of which a nozzle array for ejecting ink and a nozzle array for ejecting printing improvement liquid are arranged in parallel relationship on a common face. FIG. 3A shows a face of a black ink head 2, in which the nozzle array for ejecting a Bk (black) ink and the nozzle array for ejecting the printing improvement liquid are arranged in combination. FIG. 3B shows a face of a color ink head 3, in which the nozzle arrays for ejecting inks of respective colors of Y (yellow), M (magenta) and C (cyan) and the nozzle arrays for ejecting printing improvement liquids are arranged in combination. As shown in FIG. 3B, the nozzle arrays for respective colors of inks in the color ink head 3 are aligned with the corresponding nozzle arrays of the printing improvement liquids in parallel relationship. Adjacent nozzle arrays are spaced away from each other with a predetermined distance therebetween. Both of black ink head 2 shown in FIG. 3A and the color ink head 3 shown in FIG. 3B are scanned in a direction of arrows 6 and 7 by means of not shown carriages. The respective nozzle arrays are arranged in directions perpendicular to the scanning direction. When the nozzle arrays are scanned in the direction of arrow 6, the printing improvement liquids are ejected toward the printing paper as the printing medium in advance of ejection of the inks, and when the nozzles are scanned in the direction of arrow 7, the inks are ejected toward the printing paper in advance of the printing improvement liquid.
In the ink-jet printing apparatus, the ink and the printing improvement liquid are ejected at the same region in the scanning direction. Therefore, it is typical to make an ejection speed of the ink and an ejection speed of the printing improvement liquid equal to each other.
FIG. 5 is a side elevation diagrammatically illustrating a condition of deposition of the rebounded droplet of the printing improvement liquid ejected from the ink-jet printing head having the nozzle arrays arranged in parallel as shown in FIGS. 3A and 3B, on the face of the head at the region shifted within a predetermined period. Here, an example where the printing improvement liquid is ejection in advance of ejected of the ink will be explained.
In FIG. 5, the reference numeral 1 denotes an ink-jet printing head (hereinafter referred to as head), and 5 denotes a printing paper as a printing medium. On the printing paper 5, the droplet of the printing improvement liquid is already deposited. Before the printing improvement liquid deposited on the printing paper 5 is absorbed in the latter, the ink droplet D3 is ejected toward a region S3 where the printing improvement liquid droplet is deposited. When the ink droplet D3 is ejected to the region S3 where the printing improvement liquid droplet is deposited, the printing improvement liquid in the region S3 is not yet absorbed in the printing paper 5. Therefore, the rebounding P of the printing improvement liquid can be caused by impact of the ink droplet D3' on the printing paper 5. Among the rebounded droplet P of the printing improvement liquid, some of the rebounded droplet P' may fly toward the face 4 of the head 1. When the head 1 is scanned up to the region of 1', the rebounded droplet P' can deposit on the face 4 of the head as a rebounded droplet P".
The printing improvement liquid deposited on the face 4 of the head may be admixed with the ink droplet deposited on the face 4 as a mist or the ink droplet to be ejected at next ejection timing to cause fixing. In addition to the rebounded droplet, the printing improvement liquid may deposit on the face 4 also as a mist.
The printing improvement liquid thus fixed on the face 4 of the head 1 may cause plugging of the nozzle to result in ejection failure or deflection of the ejecting direction. Also, in case of the printing apparatus having a wiper blade wiping the face 4, damaging of the wiper blade or insufficient wiping can be caused.